Last Sunday's upper level low resulted in a little rain, mostly south of the L.A. basin, but Southern California and much of the West has been dry, dry, dry. How dry? Take a look at this plot of percent of average precipitation for the past 90 days from the Western Regional Climate Center.

Downtown Los Angeles (USC) has not recorded measurable rain for more than a month. The last measurable rain was on December 17 when 0.01 inch recorded. The water year precipitation total for Los Angeles has been stuck on 3.76 inches, which is about 2.5 inches below normal. The Sierra has been especially dry. The Statewide Summary of Snow Water Content for January 18 reported the snowpack at 10% of normal. Remarkably, Mammoth Mountain recorded no natural snow between December 5 and January 19!

The good news is the very stubborn West Coast ridge has finally relented, opening the door to a more zonal flow and a sequence of shortwave troughs. The change in pattern is forecast to produce significant rain and snow over most of the West Coast the next few days. The HPC 5-day Precipitation Forecast indicates up to about 5 inches of precipitation in some areas of the Sierra and North Coast, and over 9 inches in some areas of the Pacific Northwest.

The change in pattern isn't forecast to produce much rain south of Pt. Conception, but at this point just about any amount would be helpful. BUFKIT analysis of WRF Ensemble forecasts for Van Nuys indicate precipitation amounts ranging from about 0.1 inch to 0.5 inch, beginning sometime this evening and ending midday Saturday. The 18z NAM precipitation forecast for Van Nuys projects about 0.25 inch for the storm. Some mountain areas could see somewhat higher precipitation totals, particularly those with a west-facing aspect.

Another shortwave is forecast to move through the area Monday. Model projections differ, but we could get a little rain out of that system as well. We'll see!

Update January 25, 2012 8:00 am PST. Precipitation totals across the area from Monday's system generally ranged from about 0.3 inch to 0.75 inch. Downtown Los Angeles (USC) recorded 0.62 inches for the storm. This combined with the 0.68 inches from Saturday's system boosted the water year total for Los Angles to 5.06 inches, which is about 75% of normal for the date. The medium range models have been all over the place. Yesterday the 12z GFS forecast for Monday morning depicted an upper low and trough on the West Coast, while the ECMWF indicated some ridging. Here's a GFS/ECMWF comparison from San Jose State University Meteorology. Given the recent Sudden Stratospheric Warming (SSW) and rejuvenation of the MJO there's plenty of uncertainty in the medium range. The ECMWF seems to like the idea of a relatively fast-moving trough affecting the West Coast sometime around February 1. We'll see!

Update January 21, 2012 1:30 pm PST. Perhaps because its jet stream dynamics were more favorable than expected, this first system was a little stronger and held together a little better south of Pt. Conception than suggested by the models. Rainfall totals tabulated by the NWS generally ranged from about 0.2 to 0.7 inch in the Los Angeles area, with somewhat higher totals recorded in Ventura County and Santa Barbara County. Model projections have varied on the strength of the system forecast to move through the area on Monday. The 12z NAM projected about 0.4 inch for Van Nuys; the 18z NAM about 0.3 inch, and the 12z GFS about 0.5 inch. The system appears similar to today's, but it looks like the shortwave trough and vortex max may track more directly into Southern California.

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

Following is a chart comparing the 2011-12 La Nina to other cold ENSO episodes that have occurred since 1949. With the exception of 1961-62 and 2008-09 the cold episodes are based on the Oceanic Niño Index (ONI) and are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. A description of the parameters follows the chart. A GWO phase space plot is included for those cold episodes for which AAM data is available. Data for 2011-12 will be updated periodically.

Year

Nov-MarAAM

Peak MEI4

Peak MEI Season

PeakONI

Peak ONI Season

L.A. Rain

GWOPhase Plot

1949-501,2

--

-1.423

APRMAY

-1.7

DJF

9.94

--

1950-511

--

-1.247

NOVDEC

-1.0

NDJ, DJF

8.21

--

1954-551

--

-1.578

MAYJUN (54)

-1.2

ASO

11.94

--

1955-561

--

-2.276

MAYJUN (55)

-2.0

OND

16.00

--

1956-571

--

-1.516

MAYJUN (56)

-0.9

SON, OND

9.54

--

1961-623

-0.513

-1.093

DECJAN

-0.6

ASO, SON

18.79

1962-63

-1.259

-0.843

JANFEB

-0.7

OND, NDJ

8.38

1964-65

-1.145

-1.496

JULAUG

-1.2

SON, OND

13.69

1967-68

-0.770

-1.060

APRMAY

-0.9

JFM

16.58

1970-71

-0.976

-1.898

MARAPR

-1.3

DJF, JFM

12.32

1971-72

-0.173

-1.463

AUGSEP

-1.0

OND

7.17

1973-74

-1.331

-1.942

DECJAN

-2.1

NDJ

14.92

1974-75

-0.842

-1.255

OCTNOV

-0.9

OND

14.35

1975-76

-0.713

-2.000

SEPOCT

-1.7

OND, NDJ

7.22

1984-85

-0.597

-0.743

APRMAY

-1.1

NDJ

12.82

1988-89

-1.139

-1.591

AUGSEP

-1.9

OND, NDJ

8.08

1995-96

-0.227

-0.644

DECJAN

-0.7

OND to JFM

12.46

1998-99

-0.541

-1.233

JANFEB

-1.4

NDJ, DJF

9.09

1999-00

-0.781

-1.242

JANFEB

-1.6

NDJ, DJF

11.57

2000-01

-0.795

-.755

OCTNOV

-0.7

NDJ

17.94

2007-08

-1.010

-1.631

FEBMAR

-1.4

DJF, JFM

13.53

2008-093

-0.596

-.783

SEPOCT

-0.8

DJF

9.08

2010-11

-0.596

-2.037

AUGSEP

-1.4

SON, OND, NDJ

20.20

2011-125

-0.370

-1.046

DECJAN

-1.0

OND, NDJ

8.19

1. AAM and AAM tendency anomaly data not available.2. Based on ONI values beginning with DJF 1949-50.3. ONI did not meet threshold of 5 consecutive overlapping seasons.4. MEI values are normalized and may change as new data is added. Specified values were current as of April 24, 2012.5. Data as of April 24, 2012.

Nov-Mar AAM: The mean of the global relative atmospheric angular momentum anomaly for the period November 1 to March 31 of the following year. Data is from the GWO phase space data file linked on the Global Synoptic Dynamic Model page of the PSD Map Room Climate Products. Reference Weickmann and Berry, 2008.

There's been no rainfall recorded at Downtown Los Angeles (USC) since December 17 when 0.01 inch recorded. Los Angeles ended December with 1.01 inch of rain. This is less than half of normal for the month and far less than last December's deluge of 10.23 inches.

Even though December 2011 was somewhat dry, it comes nowhere near setting a record. Since 1877 there have been eight Decembers in which no rain was recorded, and 44 Decembers with 1.01 inches of rain or less.

Downtown begins 2012 with a water year rainfall total of 3.76 inches. Last year we would have said this was near normal, but using the new normals derived from 1981-2010 data the total is 0.56 inch below normal. It has been several years since Downtown Los Angeles (USC) recorded below normal rainfall for the first six months of the water year. The last time was July 1 to December 31, 2007.

The MJO has been relatively active this autumn and after going on a two week holiday appeared to be more coherent as it moved into the Western Pacific between Christmas and New Year's. However the NCEP GEFS and several other models forecast the MJO to rapidly diminish in amplitude and eastward propagation.

The November 30 - December 1, 2011 downslope windstorm felled thousands of trees, produced multi-day power outages and resulted in millions of dollars of damage in valley communities along the San Gabriel Mountains. An initial analysis of the conditions leading up to the event suggest a combination of factors contributed to the strength of the winds. Among them were a highly amplified and energetic north-south upper flow which was evolving into a cutoff upper low over southeastern California; a deepening surface low south of Las Vegas; cold air advection; and a possible inversion near mountain-top level.

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

The information presented on this web site may include errors of transcription, interpretation, and other errors.
The information may be out of date or inaccurate. Please refer to the NATIONAL WEATHER SERVICE FORECAST OFFICE LOS ANGELES
or your local weather service office for official forecasts and warnings.